At present, various types of nanoparticles have been used in many applications. For example, nanoparticles such as metal nanoparticles, oxide nanoparticles, nitride nanoparticles and carbide nanoparticles are used in the production of sintered bodies for use as electrical insulation materials for semiconductor substrates, printed circuit boards, various electrical insulation parts and the like, materials for high-hardness and high-precision machining tools such as cutting tools, dies and bearings, functional materials for grain boundary capacitors, humidity sensors and the like, and precision sinter molding materials, and in the production of thermal sprayed parts such as engine valves made of materials that are required to be wear-resistant at a high temperature, as well as in the fields of electrode or electrolyte materials and various catalysts for fuel cells.
It is known that among various nanoparticles, silver nanoparticles are used for various devices such as solar cells and light emitting devices, conductive pastes, electrodes for electronic components such as laminated ceramic capacitors, wiring on printed circuit boards, wiring on touch panels, flexible electronic paper and the like. Silver electrodes and silver wiring can be obtained through the process of baking silver nanoparticles. Silver nanoparticles and production methods thereof are disclosed by Patent Literatures 1 and 2, for example.
Patent Literature 1 describes the ultrafine particle producing process that introduces and disperses materials for producing ultrafine particles into a thermal plasma flame under reduced pressure using an inert gas as a carrier gas to form a vapor-phase mixture, introduces a gas mixture of hydrocarbon gas and a cooling gas other than the hydrocarbon gas in a supply amount sufficient for quenching the vapor-phase mixture toward an end portion (tail portion) of the thermal plasma flame at an angle of more than 90° but less than 240° with a perpendicular direction parallel to the thermal plasma flame and at an angle of more than −90° but less than 90° with respect to the central portion of the thermal plasma flame in a plane orthogonal to the perpendicular direction of the thermal plasma flame to generate ultrafine particles, and allows the generated ultrafine particles to come into contact with the hydrocarbon gas so as to produce the ultrafine particles whose surfaces are coated with a thin film formed of a hydrocarbon compound. Patent Literature 1 describes that ultrafine silver particles are produced using the above-described production method.
Patent Literature 2 describes silver powder having a D50 value of 60 nm to 150 nm as determined by the image analysis of a scanning electron microscope (SEM) image, having a carbon (C) content of less than 0.40 wt % as determined in accordance with JIS Z 2615 (General rules for determination of carbon in metallic materials), and comprising spherical or almost-spherical silver powder particles. Patent Literature 2 teaches that the silver powder can be sintered at a temperature of 175° C. or lower.